摘要
蚯蚓肠道内小分子有机酸与摄入的土壤矿物相互作用,加速矿物溶解。摄入的土壤在蚯蚓肠道内平均停留时间约为12 h,不足以使土壤矿物产生显著的溶解特征,因此这一过程难以在蚯蚓体内进行评估。本研究通过体外实验控制pH值和有机酸浓度,模拟蚯蚓肠道中有机酸对土壤中常见矿物的溶解反应,探讨了方解石和钾长石在蚯蚓肠道环境中的初始溶解动力学。研究发现,矿物在混合有机酸中的溶解速率比在纯水中高一个数量级,说明有机配体和质子促进了矿物溶解。溶解速率及粒度分析表明,方解石(CaCO_(3))溶解速率不受溶解过程中粒度变化的影响,而钾长石(KAlSi_(3)O_(8))粒度在溶解期间未出现显著变化。在此基础上,采用初始速率法模拟了钾长石的初始溶解动力学,计算得出的溶解速率表明钾长石在溶解初期主要为表面K^(+)的释放。使用缩核模型(shrink core model)和Hixson⁃Crowell模型对方解石溶解过程进行动力学解析,发现方解石的溶解主要受溶液中反应物内扩散的速率影响。这定量描述了两种矿物在有机酸溶液和纯水中的溶解差异。现有研究表明,有机配体和质子协同促进了矿物的溶解,同时进一步说明蚯蚓肠道加速了土壤矿物的溶蚀以及矿物元素的释放。
Earthworms decompose ingested earth materials through interactions of small molecular organic acids with minerals to accelerate soil weathering.This process is difficult to be assessed in vivo because the average residence time of soils inside earthworm gut is on the scales of 12 hours,too short for minerals to exhibit sizable and visible dissolution features.In present study,earthworm weathering of calcite(CaCO_(3))and K⁃feldspar(KAlSi_(3)O_(8))is investigated in vitro using a mixed organic acid solution at pH 7 mimicking the composition and pH conditions of gut fluid.Experimental results showed that the dissolution rates experienced one order of magnitude increase relative to that in pure water,suggesting the occurrence of organic ligand⁃promote weathering.The observed correlation of dissolved cation concentrations to mineral particle sizes for calcite but not feldspar suggests the former dissociates directly in accordance with the stoichiometry while the latter dissolves following an incongruent pathway.Based upon this understanding,we further examined the dissolution kinetics using the initial rate method for feldspar and the shrink core model in conjunction with the Hixson⁃Crowell equation for calcite.The theoretical analyses indicate feldspar dissolution initiates as K+release from mineral surfaces whereas calcite weathering is chiefly limited by the rate of reactant diffusion in solutions.These findings are in agreement with the known mechanistic framework for calcite and feldspar dissolution,but showcase the importance of ligands,instead of protons,to earthworm digestion of minerals in vivo.
作者
蔡建林
TENG Hui Henry
王钺博
张坚超
CAI Jian-lin;TENG Hui Henry;WANG Yue-bo;ZHANG Jian-chao(Institute of Surface-Earth System Science,School of Earth System Science,Tianjin University,Tianjin 300072,China)
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2022年第4期818-834,共17页
Acta Petrologica et Mineralogica
基金
国家自然科学基金项目(41830859,41702035)。
关键词
蚯蚓
有机酸
方解石
钾长石
风化
earthworm
organic acids
calcite
potassium feldspar
weathering
